title: Repeated exposure of goldfish (Carassius auratus) to tricaine methanesulfonate (MS-222).
abstract: Goldfish that have been repeatedly exposed to tricaine methanesulfonate (MS-222) require greater concentration of the drug to attain equivalent planes of anesthesia, but the mechanism for this increased anesthetic need is unknown. Minimum anesthetic concentration (MAC) is a commonly used method with which to compare anesthetics. It was hypothesized that fish exposed to MS-222 daily would have an increased MAC. It was also hypothesized that fish exposed daily to MS-222 would develop histomorphologic changes to their gills to explain the increasing demand. Forty-nine Serasa comet goldfish were enrolled and were divided into three populations (n = 15, n = 15, and n = 19). In trial 1, using an up-down method, MAC was determined daily after 4 min of exposure to MS-222 for which the starting concentration was 160 mg/L. In trial 2, MAC was determined following 2 min of exposure to MS-222 for which the starting concentration was 260 mg/L. In trial 3, four naive fish were euthanatized and gills collected for histology and electron microscopy (EM). The remaining fish were exposed to MS-222 daily for 4 wk. Four fish were euthanatized and their gills submitted for similar examination at 2 wk and 4 wk. MAC for fish exposed to MS-222 for 4 min increased from 120 to 160 mg/L. The regression line had a slope of 1.51 +/- 0.26 (R2 = 0.65; P < 0.0001). MAC for fish exposed to MS-222 for 2 min increased from 210 pmm to 220 mg/L; the regression line had a slope of 0.52 +/- 0.38 (R2 = 0.12; P = 0.2). Histologic and EM examination of gills did not show morphologic changes indicative of a reaction to MS-222. Goldfish in this study had an increased requirement for MS-222 following daily exposure for 4 min but not following daily exposure for 2 min at a higher concentration. The cause of this increased anesthetic need is not related to morphologic changes to the gills.
authors.affiliation: Department of Molecular and Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, North Carolina 27607, USA. lpposner@ncsu.edu
authors.forename: Lysa Pam
authors.initials: LP
authors.lastname: Posner
authors.forename: Gregory N
authors.initials: GN
authors.lastname: Scott
authors.forename: J McHugh
authors.initials: JM
authors.lastname: Law
mesh_terms: D062365:Aminobenzoates / Q000008:administration & dosage* / Q000009:adverse effects / Q000494:pharmacology*; D000777:Anesthetics / Q000008:administration & dosage* / Q000009:adverse effects / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005393:Fish Diseases / Q000139:chemically induced; D005880:Gills / Q000187:drug effects / Q000473:pathology / Q000648:ultrastructure; D006054:Goldfish
chemical_list: D062365:Aminobenzoates; D000777:Anesthetics; C003636:tricaine